The present invention relates to a deinking agent to be used for the reclamation of waste papers such as newspapers and magazines. More particularly, the present invention relates to a deinking agent that yields a deinked pulp having a high b value and showing good defoaming properties of a flotation reject can be obtained by deinking, for example, newspapers or magazines according to a combination of the flotation and washing methods.
It has long been a practice to reclaim waste papers such as newspapers and magazines. Recently the effective utilization of waste papers has become important in conjunction with the problems of the shortage of pulp resources and an increase in the cost thereof. Further, it has been attempted to use deinked pulp in the production of higher quality products. On the other hand, recent improvements in printing techniques, printing systems and printing ink compositions, as well as the utilization of waste papers that have never been reclaimed before, have made it difficult to deink waste papers. In order to facilitate deinking, therefore, attempts have been made to improve deinking devices. In order to remove inks and other impurities from waste paper, there have been used alkaline agents such as caustic soda, sodium silicate, sodium carbonate and sodium phosphate, bleaching agents such as hydrogen peroxide, hydrosulfites and hypochlorites, and sequestering agents such as EDTA and DTPA together with deinking agents including anionic surfactants such as alkylbenzenesulfonates, higher alcohol sulfates, .alpha.-olefinsulfonates and dialkyl sulfosuccinates, ethylene oxide adducts of higher alcohols, alkylphenols and fatty acids, and nonionic surfactants such as alkanolamides, either alone or in the form of a mixture thereof. Although these deinking agents show excellent foaming properties in the flotation treatment, their ability to collect ink is limited. In the washing method, on the other hand, these drinking agents are poor in detergency and the good foaming properties thereof cause trouble in draining. As a result, only a deinked pulp of a low grade can be obtained. Furthermore, even when a pulp of a high whiteness is obtained, a dull color remains to restrict the utilization of the deinked pulp (for example, employed in a decreased amount under the surface of cardboard or added in a decreased amount to newspapers), or so as to do the amount of a bleaching agent must be increased to eliminate away with the dullness. In order to obtain a deinked pulp which is free from dullness and has a light color tone, it is necessary to elevate the b value. Although the b value can be elevated by using a large amount of alkali, other problems such as increases in sticky matters, the draining load and the brittleness of the obtained pulp may occur in this case. Thus no effective means has been known for solving these problems.
The present inventors proposed the use of a reaction product obtained by adding an alkylene oxide to a mixture of a natural fat and a trihydric or higher alcohol as a deinking agent (cf. Japanese Patent Laid-Open No. 239585/1985).
As the result of investigations on the behaviors of such a reaction product in a deinking process, however, disadvantages were recognized. That is, a compound obtained by using a natural fat and a trihydric or higher alcohol at a molar ratio of from 1:0.5 to 1:3 frequently cause foaming problems in the flotation, dehydration, draining and papermaking stages. Further, the deinked pulp thus obtained was not completely free from a dull color, though it had a high whiteness.